ABSTRACT
Since the cruise of H.M.S. Challenger (Haeckel, 1887), modern Radiolaria have been known to represent quite diversified assemblages, compared to other microplanktonic groups such as planktonic foraminifera of which there are about 40 present day species in the world (B^, 1977). The diversity and geographic or vertical distribution of living Radiolaria remained, however, largely unknown until twenty years ago when sediment traps began to be more widely used in the Atlantic and Pacific Oceans. One of the first reliable estimates reported about 200 radiolarian species from a single geographic area in the tropical Atlantic (Takahashi and Honjo, 1981). Ten years later, Takahashi (1991) reported 182 Nassellaria and 175 Spumellaria from 4 trapping sites in tropical areas of both the Adantic and Pacific Oceans. A survey of all sediment trap and haul studies, including tropical, Antarctic and Arctic domains, currendy gives a total of 269 nassellarian and 210 spumellarian species. These numbers must, however, be considered as under-representative since many living taxa are not yet well described.
